how can i reverse this!!??

[Potemkin]

hi,

i have created a encyption where you enter in an integers and it uses this formula to encrypt it (number + number + 7) % 10

now if i plug in 1 2 3 4 as my numbers

(1 + 1 + 7) % 10 is 9
(2 + 2 + 7) % 10 is 1
(3 + 3 + 7) % 10 is 3
(4 + 4 + 7) % 10 is 5

encryption is 9135

how do i decrypt it to get back to 1234?

thanks,
john

[laserlight]

There is no reverse operation for modulo.

[leatherback]

You cannot, since it doesn't create a unique output:
orig. - > encrypt:
1 -> 9
2 -> 1
3 -> 3
4 -> 5
5 -> 7
6 -> 9
7 -> 1
8 -> 3
9 -> 5*

[Merve]

I don't think you can really decrypt your formula because the remainder of a number divided by 10 can change. However, you can list the possibilites of the decrypted formula, since you know that 0 will give seven, 1 will give nine, 2, will give one, etc.

For example, 9135 could decrypt to:
1234
1239
1284
1289
... and so on.